[PATCH] rmap 3 arches + mapping_mapped

From: Hugh Dickins <hugh@veritas.com>

Some arches refer to page->mapping for their dcache flushing: use
page_mapping(page) for safety, to avoid confusion on anon pages, which will
store a different pointer there - though in most cases flush_dcache_page is
being applied to pagecache pages.

arm has a useful mapping_mapped macro: move that to generic, and add
mapping_writably_mapped, to avoid explicit list_empty checks on i_mmap and
i_mmap_shared in several places.

Very tempted to add page_mapped(page) tests, perhaps along with the
mapping_writably_mapped tests in do_generic_mapping_read and
do_shmem_file_read, to cut down on wasted flush_dcache effort; but the
serialization is not obvious, too unsafe to do in a hurry.

4 files changed, 27 insertions, 12 deletions

diff --git a/include/asm-arm/cacheflush.h b/include/asm-arm/cacheflush.h
index 6968e8e90c3e..91b16cc3f502 100644
--- a/include/asm-arm/cacheflush.h
+++ b/include/asm-arm/cacheflush.h
@@ -283,23 +283,19 @@ flush_cache_page(struct vm_area_struct *vma, unsigned long user_addr)
  * flush_dcache_page is used when the kernel has written to the page
  * cache page at virtual address page->virtual.
  *
- * If this page isn't mapped (ie, page->mapping = NULL), or it has
- * userspace mappings (page->mapping->i_mmap or page->mapping->i_mmap_shared)
- * then we _must_ always clean + invalidate the dcache entries associated
- * with the kernel mapping.
+ * If this page isn't mapped (ie, page_mapping == NULL), or it might
+ * have userspace mappings, then we _must_ always clean + invalidate
+ * the dcache entries associated with the kernel mapping.
  *
  * Otherwise we can defer the operation, and clean the cache when we are
  * about to change to user space.  This is the same method as used on SPARC64.
  * See update_mmu_cache for the user space part.
  */
-#define mapping_mapped(map)	(!list_empty(&(map)->i_mmap) || \
-				 !list_empty(&(map)->i_mmap_shared))
-
 extern void __flush_dcache_page(struct page *);
 
 static inline void flush_dcache_page(struct page *page)
 {
-	if (page->mapping && !mapping_mapped(page->mapping))
+	if (page_mapping(page) && !mapping_mapped(page->mapping))
 		set_bit(PG_dcache_dirty, &page->flags);
 	else
 		__flush_dcache_page(page);
diff --git a/include/asm-parisc/cacheflush.h b/include/asm-parisc/cacheflush.h
index 52b0c6a96aea..7a77986e3738 100644
--- a/include/asm-parisc/cacheflush.h
+++ b/include/asm-parisc/cacheflush.h
@@ -69,8 +69,7 @@ extern void __flush_dcache_page(struct page *page);
 
 static inline void flush_dcache_page(struct page *page)
 {
-	if (page->mapping && list_empty(&page->mapping->i_mmap) &&
-			list_empty(&page->mapping->i_mmap_shared)) {
+	if (page_mapping(page) && !mapping_mapped(page->mapping)) {
 		set_bit(PG_dcache_dirty, &page->flags);
 	} else {
 		__flush_dcache_page(page);
diff --git a/include/asm-sh/pgalloc.h b/include/asm-sh/pgalloc.h
index bd02728a69d5..4584c9e37a75 100644
--- a/include/asm-sh/pgalloc.h
+++ b/include/asm-sh/pgalloc.h
@@ -101,8 +101,8 @@ static inline pte_t ptep_get_and_clear(pte_t *ptep)
 		unsigned long pfn = pte_pfn(pte);
 		if (pfn_valid(pfn)) {
 			page = pfn_to_page(pfn);
-			if (!page->mapping
-			    || list_empty(&page->mapping->i_mmap_shared))
+			if (!page_mapping(page) ||
+			    !mapping_writably_mapped(page->mapping))
 				__clear_bit(PG_mapped, &page->flags);
 		}
 	}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c7f0052b4abd..3d7c320d675e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -374,6 +374,26 @@ struct block_device {
 int mapping_tagged(struct address_space *mapping, int tag);
 
 /*
+ * Might pages of this file be mapped into userspace?
+ */
+static inline int mapping_mapped(struct address_space *mapping)
+{
+	return	!list_empty(&mapping->i_mmap) ||
+		!list_empty(&mapping->i_mmap_shared);
+}
+
+/*
+ * Might pages of this file have been modified in userspace?
+ * Note that i_mmap_shared holds all the VM_SHARED vmas: do_mmap_pgoff
+ * marks vma as VM_SHARED if it is shared, and the file was opened for
+ * writing i.e. vma may be mprotected writable even if now readonly.
+ */
+static inline int mapping_writably_mapped(struct address_space *mapping)
+{
+	return	!list_empty(&mapping->i_mmap_shared);
+}
+
+/*
  * Use sequence counter to get consistent i_size on 32-bit processors.
  */
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)